(function (tree) {

tree.Extend = function Extend(selector, option, index) {

this.selector = selector;
this.option = option;
this.index = index;
this.object_id = tree.Extend.next_id++;
this.parent_ids = [this.object_id];

switch(option) {
    case "all":
        this.allowBefore = true;
        this.allowAfter = true;
    break;
    default:
        this.allowBefore = false;
        this.allowAfter = false;
    break;
}

}; tree.Extend.next_id = 0;

tree.Extend.prototype = {

type: "Extend",
accept: function (visitor) {
    this.selector = visitor.visit(this.selector);
},
eval: function (env) {
    return new(tree.Extend)(this.selector.eval(env), this.option, this.index);
},
clone: function (env) {
    return new(tree.Extend)(this.selector, this.option, this.index);
},
findSelfSelectors: function (selectors) {
    var selfElements = [],
        i,
        selectorElements;

    for(i = 0; i < selectors.length; i++) {
        selectorElements = selectors[i].elements;
        // duplicate the logic in genCSS function inside the selector node.
        // future TODO - move both logics into the selector joiner visitor
        if (i > 0 && selectorElements.length && selectorElements[0].combinator.value === "") {
            selectorElements[0].combinator.value = ' ';
        }
        selfElements = selfElements.concat(selectors[i].elements);
    }

    this.selfSelectors = [{ elements: selfElements }];
}

};

})(require(‘../tree’));